Bonsoir,
1)
Pour x = 3 AB = 7
AF² = AB² + AE² = (2x+1)² + (x + 3)² = 7² + 6² = 85
AF = √85 ≈ 9.22
2)
Aire EFCD = EF * ED = 1 * 7 = 7
3)
pour x > 2
3)
ED = AD - AE = (2x+1)-(x+3) = x - 2
4)
Aire EFCD = (2x+1)(x-2) = 2x² - 3x - 2
5)
Aire ABCD = (2x+1)² = 4x² + 4x + 1
Aire ABFE = (2x + 1)(x + 3) = 2x² + 7x + 3
6)
Aire EFCD = Aire ABCD - Aire ABFE = (4x² + 4x + 1) - ( 2x² + 7x + 3)
Aire EFCD = 2x² - 3x - 2
Bonne soirée